Two-way repeating circuit



Dec. 23, 1941.

L. EsPENscHlE-D ETA;

TWOf-WAY REPEATING CIRCUIT' Filed April 18, 1940 2 sheets-sheet i AAI A rr'oRA/EV TWO`-WAY REPEATING CIRCUIT Filed April 18, 1940 2 Sheets-Sheet 2 /Of www EAST FIG.9 "E" .41.. EsPENscH/Eo /NVENTORSR ENZ I ATTORNEY Patented Dec. 23, 1941 Two-WAY REPEATINGCIRCUirr Telephone Laboratories, `Incorporated, 'New York, N.`Y., a. corlwration of New York 1 i N Application April 1s, 1940; `sri`a1`No. sedation 8 claims. (QI. 1ra-'170i` 1 v This invention relates to the Vtransmission of electric currents, and aims to provide simple and efficient means `for accomplishing such transmission,, especially overcircuits used fortwo-way signaling overfasingle conductor pair. p `In a form of the invention which is shown i theaccompanyin-g drawings, a two-way electron dischargerepeater has the `output of each of its` oppositely directed amplifying paths so connected to the input of the other of these paths as1to deliver to the grid of an electron discharge device ini this other path a potential tending to prevent theA transmission through this..other path, to'thereby` prevent singing of the repeating elements due lto currents from one ofthe amplifying paths circulating `through the oppositely directed amplifying'path.` This is to be accomplished without requiring mechanical switching means at-the repeater or other usual forms .of singing suppressors.A The repeater is connected in a line to which is connected means for sending alternating signal `currents which initiate reactions for conditioning the repeater to faithfully repeat `the alternating currents in the desired direction and to block transmission in the opposite direction. These and variousother features'of` the invention will be pointed.` out by reference to the drawings in which: Y

Fig. `1 shows schematically a repeater' embodying one-form of our invention;

Fig. 2 is a modification thereof;

Fig. 3 is a modified form of repeater tube over that shown in Fig. 1 by which the objects of our invention may be attained; 4 is a still further modiiication with certain circuit connections; 5,is an extensionof the circuit of Fig. 1i Fig. 6 shows the introduction of the repeater of Fig. 1 in a transmission line; and

Figs. 'l to 9 are modifications of Fig. 6.

I Referring more particularly to Fig. 1, there is shownV the repeater point of a transmission line adapted for two-way communication from west to east 'and east to West. The repeater here shown consists of an electron discharge tube of special structure, all in one envelope, with a 'plurality of grids for performing functions described below. The tube structure is essentially a double vacuum tube amplified one of the tubes acting as anampliiier for transmission in'the one It'also comprises an 'amplier 'with the common cathode afrplate` dHand `grids bfva rior` transmission., from east to westl Br'dged, across the line on5the output sidegof` thefrfst` ampli; fier `is the battery B and the load R. Similarly, B `and 1-1.'` are connected tothe, output 4of the other Vamplifier."` Across rthe input of the` tube is connected-the gridleak I2 and biasing'. battery I3.. rIt will be noted that Vthere isa cross-- connection whereby-the grid b is` connectedfto the plate dand the grid b is connected -to thel plate d.` In each of these connections there is a biasing battery I8. and a condenserj5,1shuntedl` by aresistance I-6. i y

The operation of the circuit` is as follows; The biasingloflthe ampliiiers bythe gridsbandb is such that a small, but avery small, .current` is ilowingpl When signal arrives from thewwest it isA impressed on thejgrid Very early in the signal-traina positive impulsewill reach crcausfA ing a .substantial increase in the ,current to the plate d.A This causesa droppin thepotential of the plat-e, `which is very quickly transferred4 Hto thegrid JJ". :'I'hislowering-in .the potential .of b decreases the current flowing to d'5. whereupon the potential of d? rises. increasesin potentialgis very` quickly transferredto the grid b. This increasesthespace current :to the" plate d, bringingthe tubeto a-,more favorable portion of its operating characteristic, resulting in a fure ther drop in the potential of the plated and a further drop in the potentialof b'. Whenthe positive impulse in thesignal train gives way to a. negative pulse `the `sequence of `operations on thelplate d reverses,` but this timefithe effect of` electron conduction from` anode d lto grid b' prevents a reversal `of its potentialabout itsbias point, and it retains a measure ofthe potential lowering incurred in the previous process. As a lresult of successive positive and negative, impulses' in `the' signal, therefore, `there is a cumulative lowering of the potentialof grid b. This leads to a cumulative decrease inthe current iiowing` to plate d', and a corresponding 4cumulative rise inlthe potential of d', a cumulative rise in the potential of gridb, and a rise in the spacecurrent to plate d. The cumulative process occursat a greater rateas the risey in space current to d `increasesv the gain from grid c to plate=` d, and rapidlyl places av bias on b.' sufficiently large# to suppress currentto the plate d' so that itspotential becomes substantially` the same as thefpotential of the battery B and this corresponds toa large positivebias offtlie grid b. yFrom the above it"isseenthat` signal ,com-

tiated first from the east, will be transmitted to .the West and will block transmission of signal from the west to east. The size of the capacities and the resistances and the biasing batteries will be such that the speed of building up of ampliiication in the desired direction is very high but the rate at which the circuit returns to idle condition is relatively low. The speeds may be varied over a wide latitude, but preferably the decay time should besuch as not to respond to the usual intervals between syllables but definitely be responsive to terminations of sentences.

From the above it v vill be observed that as the electron stream in the one path increases, that in the other decreases, or expressed in other terms, as the gain in the one tube increases, the gain in the other decreases. Normally, when no signal is being received, the gain of the tubes is' so low that singing does not take place nor at any time during the reception of signals is the total gain around the total repeater section sufiicient to permit singing. While a definite time is required to condition the repeater for full gain in one` direction this time is very small, for the iirst positive impulse, arriving for example on the grid c, will increase the electron stream lowering the potential of d and b'. This is almost instantaneously accompanied by a raising of the potential of d and b. After only a few of the initial Waves of the wave train have been received the electron stream to d will have been reduced to zero and the grid b will have reached its maximum value corresponding to a gain saturation in the electronv path to d.

" While in Fig. `1 the tube has been described as one of special construction with all elements included within one envelope, this disposition of elements is not necessary but the -two yparts of the tube may be made up separately. This is lshown in Fig. 2 in which corresponding parts are correspondingly indicated. The operation of the circuit is precisely the same.

A modiiication of the tube circuit of Fig. 1 is shown in Fig. 3. The tube here is essentially of the'cathode ray type of 'tube comprising an electron source a and anode h maintained at a constant potential giving rise to a stream of'electrons going to the plates d and d. The electron stream is suiiiciently diifuse so that while most of the electrons pass through an aperture or space betweenl electrodes d and d' someof them fall on each plate. Elements b andr b', 'in the form of deflecting plates, serve the same purpose as the grids band b' of Fig. 1.` If, for example, plate b .is given a 'positivecharga the'electron beam is so deflected as to increase the `portion falling on the electrode d and to decrease the portion falling on d'. Control grids c and c serve the same function' as the corresponding grids in Fig. 1. 'Ihe connections in circuitand the operation are identically the same asthat for Fig. l' with the exception of a iixed positive potential applied to theelement rh.

Fig.` 4 shows a further'modifica'tion of Vthe circuit of Fig. 1, use here being made of the phenomenon of secondary electron emission. The common cathode, the grids b and b and the grids c and c' operate in essentially the same manner as indicated in Fig. 1. The tube, however, instead of containing a single plate for each direction of amplification, is provided with a multiplicity of plates to which the electrons go successively, generating secondaries on each impact eX- cept the last. The external connections are made in the same way as Fig. 1, connection being lmade to the last plates dn and dn instead of d and d. It is apparent that additional three-element amplifiers in separate envelopes may be used instead of the series of plates.

Fig. 5 is an extension of the section of Fig. 1

into a push-pull combination. The analogous parts are clearly shown and the operation of the circuit will be evident. The iirst Wave in the signal train will make the one side of the circuit positive and immediately start conditioning the repeater on that side of the line for transmission in the one direction. The next half of the wave will render the other side of the line positive and will start conditioning the repeater on that side for amplification in the correct direction. The object of the push-pull connection is to secure immunity to the listening subscriber from a click which is apt to be generated just at the beginning of transmission. This click is generated by the rapid rise in space current to the amplifying side of the tube while transmission is being established. With the push-pull connection a rise in space current occurs in each tube Iand the pulses balance each other in the output. Thus the subscriber Will not hear the click.

One manner in which the repeater units may be introduced into the transmission line is shown in Fig. 6 which shows a manner of connection using the hybrid coil arrangement common in the telephone art for two-Way signaling on one pair of wires. The standard type of hybrid coils is shown at I0, I0 and N, N are the usual balancing networks. The connection within the repeater unit itself are the same as for the figures already described.

The repeater unit'may be connected directly to the line with a proper adjustment of biasing voltage, but in this case the transmission from plate d is apt to be approximately the same as from line W to grid b and there will then be a tendency for the signal from W to operate on gridb in such a direction as to reduce the amplification in the W-E direction and tend to nullify in part the operation of the mechanism as a whole. To obviate this it is desirable to introduce more loss in the line W than in the line from the plate d and to do this Without inserting loss in the path from the line W to grid c. One arrangement for effecting this is shown in Fig. 7. This consists of building a pad around the battery-feed to plate d' as shown in Fig. 7. It will be noted, however, that this reduces the output power capacity 'of the tube in the direction E-W by the same amount that it introduces losses in the path line W--grid b. To avoid this, use can be made of a conjugate network to join their respective paths, as shown in Figs. 8 and 9.

In Fig. 8, for example, this is shown as a simpliiied 'hybrid coil. The impedance Z is adjusted to match the plate circuit. If the match were perfect and the coil were perfect and symmetrical, then infinite loss would be introduced lfrom line W to grid b but only three decibels each in the paths from plate d to line W and from plate l d to grid b. In practice these ideal conditions will not obtain, but nevertheless it is possible to introduce substantially more loss from line W to grid b than from plate d to line W and to grid b.

In Fig. 9 another arrangement of a simplified coil is shown. Here again the impedanceZ is adjusted to match the plate circuit impedance and the losses introduced t the respective parts of the ycircuit are substantially the same as shown in Fig. 8. i

Referring to Fig. 6, it should be noted that in view of the use of the hybrid coils there shown,

no additional conjugate network such as shown in Figs. 8 and 9 is necessary. This is because the gain in the W-E direction through grid c and plate d can be made fairly large when the device is in the neutral-no-signal condition. It should be noted. however, that the situations in Fig. 6 and Fig. `8 are not quit identical. The hybrid coils in Fig. 6 are shown in the conventional twowire repeater connection. In Figs. 8 and 9, however, the hybrid coils control transmission through the triggering grids b rather than through th'e amplifying grids c. This' means that if any spurious voltage reaching a grid is sufficiently low to prevent its triggering wrongly, no effect whatever will be produced.

In all these arrangements it is necessary to proportion the circuit and apparatus constants such that when the circuit is idle in both directions there is a small loss in the circulating path in this condition. Where hybrid coils are used outside the amplifying element, as in Fig. 6, it is possible to have as much gain in this condition as in a conventional two-wire repeater, the gain then being raised above this value during actual transmission. It is desirable also that once the signals are received from one direction the repeater gains in the two directions should assume their proper respective values and not vary too much with the intensity of the signal once this is more than a given amount. This is evidently accomplished by the nature of the action in each circuit where the loss of gain in the suppressed direction causes increase of gain in the transmission direction and vice versa. Assuming transmission from west to east, the electron flow from cathode a to plate d approaches zero, practically disabling transmission in this direction and the potential of plate d approaches that of the positive plate of the supply battery and can go no higher. This fixes a maximum positive potential of the grid b and saturates the gain in this direction.

It is also, of course, necessary to prevent the device locking up |completely in any one direction of transmission. This is accomplished by grid leaks I6 to grids b and b which are crossconnected to the plates d and d, respectively, which bring the amplifiers back to the idle condition when no speech is received in either direction.

What is claimed is:

1. A two-way `repeater for insertion between two sections of a two-way line having only two conductors comprising space discharge apparatus including cathode means having connection to one conductor of each lin'e section, two anodes connecting individually to the opposite conductor of the respective line sections, two control grids connected individually to the respective side of the line section such that one grid and cathode means are connected across each line section, a

blocking grid for each cathode-anode space and 7 means controlled by electron flow toward either anode for blocking electron ow toward the opposite anode comprising a bias transfer conductor conductively'connecting each anode tothe blocking gridof the opposite cathode-anode space.

2. A two-way repeater for insertion between two sections of a two-way line having only two conductors comprising space discharge apparatus including cathode means having connection to one conductorof each line section, two anodes connected individually to the opposite conductor of the respective line sections, two control grids connected individually to the respective side of the line section such that one grid and the cathode means are connected across each line section, two additional grids conductively connected individually, each to the anode of the other section, such that electron flow toward either anode applies a bias voltage over the corresponding conductive connection to the additional grid of the other section for blockingfelectron flow toward the opposite anode.

3. In a two-way amplifier repeater for insertion between two sections of a two-way line having only two conductors comprising a cathode means initiating an electron stream path to an anode in each section, a grid connection toeach linesection each adapted to control the electron stream in the other section in accordance with signal variations, and means associated with the electron paths for so conditioning the electron paths that signal from the one section builds up the amplification toward the other ysection and lowers the amplification toward its own section,

said last means comprising an additional grid in` each electron path and a bias conductor connecting such additional grid to the anode of the opposite section.

4. In a two-way amplifier repeater for insertion between two sections of a two-way line having only two conductors comprising cathode means initiating an electron stream path to an anode in each section, a grid connected to each section and adapted to control the electron stream in the other section in accordance with signal variations, and means associated with the electron paths so conditioning the electron paths that when idle the gain in each electron path is very low and when signal arrives from the one section the gain toward the other section is increased and the gain toward its own section is Y decreased, said last means consisting of an additional grid in each path conductively connected to the anode of the other section and means operating in response to the arrival of signal waves for progressively increasing the gain in the one path and reducing it to substantially zero in the other path.

5. The combination of claim 4 including elements for controlling the rate of progressive increase and decrease in the gain in said paths, said elements having such time constant that the progressive increase of gain to maximum in the one path and the reduction to zero in the other occur within the time of the rst few vibrations of the signal.

6. In a two-way amplier repeater for insertion between two sections of a two-way line comprising cathode means initiating an electron stream path to an anode in each section, a grid connected to each section and adapted to control the electron stream in the other section in accordance with signal variations, and means associated with the electron paths so conditioning the electron paths that when idle the gain in each electron path is very low and when signal arrives from the one section the gain toward the other section is increased and the gain toward its own section is decreased, said last m'eans consisting of an additional Agrid in each path and means operating in response to the arrival of signal Waves for progressively increasing the gain to maximum in the one path and reducing it to substantially zero in the other path, means including elements for controlling the rate of progressive increase and decrease in the gain in said paths, said elements having such time constant that the progressive increase of gain to maximum in the one path and the reduction to Zero in the other occur Within the time of the rst few vibrations of the signal and said elements having such time constant that the restoration to normal condition of said electron paths upon cessation of signal occurs at a substantially slower rate. l

'7. A two-way amplifier repeater for insertion between two sections of a two-way line comprising a cathode ray tube having a cathode, beam forming means and two targets located one on each side of the beam in its position when no signals are received, one of said targets being connected to each section of the repeater, a pair of deflecting plates one connected to each sec tion and means operatively associated therewith and operative when signal is being transmitted in one direction to deect the beam to the proper target for that direction of transmission, a grid connected to each section and positioned to control the strength of the beam in accordance with signal variations received from one of said sections to cause an amplied replica of the signal variations to be passed on to the other section.

8. In a two-way ampliiier repeater for insertion between two sections of a two-way line, the repeater being in the form of a cathode ray tube having a cathode, means at one end initiating an electron stream, a focusing electrode through which the electron stream passes thereby being made narrower and Ycaused to travel centrally along the length of the tube, two targets representing the anodes located equidistant from the center of the other end of the stream so as to allow the stream to pass between themI when the repeater is inoperative, one of the targets being connected in each section of the repeater, a grid connection in each section adapted to control the electron stream in accordance with signal variations when said stream is directed toward the target of the other section, two deflecting plates adjacent to the electron stream one connected to 'each section of the repeater and acting under control of signals received from. the one section to deiiect the stream to the target of the other section thereby building up the amplification toward the other section and reducing the amplification toward its own section.

LLOYD ESPENSCHIED. PIERRE MERTZ. 

